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So does forced induction negate the effect of engine braking on compression motors?

For example, going down an incline, drop into 3rd (automatic) to get some engine braking going. With my new Chevy Cruze which has a turbo, it seems like it doesn't matter what I do in what gear, there just isn't any engine braking ability.

Motors are similar size 1.6 vs 1.4 (turbo)

Note: Maybe new tags like Forced-Induction, Turbo and Supercharger should be added

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@Bob Cross lol! thanks, i didn't relize my spelling mistake which greatly changes the question. –  DustinDavis Aug 23 '11 at 22:24
    
I had forgotten that edit: that made me laugh this morning. Yes, that sure would be a different question.... –  Bob Cross Jan 25 '12 at 13:31

2 Answers 2

up vote 4 down vote accepted

The turbo shouldn't have any effect here after the first fraction of a second - a turbo runs off exhaust gases so with your foot off the accelerator it will spin down, and thus giving no forced induction. I don't know if there would be an effect with a supercharger, but I'm guessing not much.

The difference in size will have an impact though 0.2 of a litre is quite a big difference in percentage terms, so it doesn't surprise me that you can feel the difference.

I get a lot of engine braking in my 2.5l turbocharged Subaru once the turbo spins down (I do have to wait for that half a second or so after taking my foot off the accelerator for it to take effect)

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I just realized that the throttle blades would be closed (mostly) so you're correct I don't see how forced induction could affect it unless it's all going through the IAC valve. –  DustinDavis Aug 23 '11 at 21:57
    
Agreed, you get plenty of engine braking on a turbocharged engine, my 3.0L I can engine brake from 70MPH to a near stop in the course of coming off the freeway, along the ramp and up to a light. As stated, 1.4L just isn't much resistance to a 3,000lb car. Plus automatics give less engine braking than manuals. –  ManiacZX Aug 23 '11 at 22:24
    
Didnt realize there was that much of a diff from a 1.6 auto to a 1.4 (turbo) 6 speed manual. –  DustinDavis Aug 23 '11 at 22:33

This may also have to do with your new vehicle more than anything else.

You didn't mention what your previous one is but did mention your new one is a Cruze. Especially if you purchased the ECO model than this may be the case.

Chevy is trying to squeeze every MPG they can out of this car, such as on the ECO manual having an "ECO overdrive gear" (just a taller gear to keep the RPMs lower when crusing on the highway).

The more commonly known items related to fuel mileage are size of the engine and weight of the vehicle.

Aerodynamics have a big play to, the more wind resistance (drag), the more work the engine has to do.

Another is rolling resistance, some tires are rated as "low rolling resistance".

All of these items to reduce fuel consumption are going to also make the feel of engine braking less as the car will coast easier on its own.

Engine braking works a lot better on a vehicle that wants to slow down on its own and so needs the engine pushing it forward to keep going.


Response to Comment

Well, again with the Eco stuff, maybe they are doing something odd.

Engine braking happens because when you let off the gas pedal at speed the car makes the choice to provide 0 fuel to the engine allowing the engine to be rotated by the rotation of the tires, unlike when stopped and you release the gas pedal it maintains an idle.

Maybe Chevy has something where the Eco still provides some fuel and continues to fire. Since consistency is one of the most important things to good fuel mileage, they may have found that normal engine braking for a standard driver was more of a hindrance.

That is all just wild guessing, I haven't read anything on that but I could see there being something behind better fuel mileage by having the vehicle better maintain its own speed and requiring the input of the brake pedal to do the stopping.

It seems like the general driver is mostly always on the gas pedal or the brake, they don't know anything else.

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It is the Eco version. Previous car was 2006 Kia Rio 1.4l Auto 4sp. Even in 4th gear though, it just keeps going. The car out of gear actually slows down faster (going down hill) then it does while in gear with no throttle. Of course, out of gear means there is no engine braking. –  DustinDavis Aug 24 '11 at 5:05

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